Roller conveyors are well known in the art and may be provided as a gravity conveyor or a powered roller conveyor where power is applied to the rollers to cause them to rotate and convey material along its length. In the prior art, different designs are generally provided by manufacturers of conveyors for each of these different types of applications. A gravity roller conveyor design does not have supporting structure for a motor, pulleys, and gearing between sections of conveyor, Therefore, the amount of steel used in the supporting structure including side frames and supports may be reduced over that in a power conveyor design. In the prior art, at least one manufacturer offers a gravity roller conveyor which may be converted to a powered conveyor by the addition of a packaged power converter including a gear motor and a belt drive which is rather bulky and when mounted to the conveyor, extends out into the aisle. The addition of the power conversion package places an additional load on the gravity roller conveyor and reduces its load carrying capacity. Thus, additional structure must be usually added to support the conveyor for use with the same amount of loading.
With applicant's design, the components for a V-belt drive may be bolted directly onto the existing framework and in the same envelope as the gravity conveyor and thereby maintain most of the load carrying capacity of applicant's gravity conveyor design. By adding the components directly to existing mounting structure in the gravity conveyor design, and by using a V-belt drive, applicant makes it feasible for a manufacturer to have a single design for a gravity roller conveyor and a powered roller conveyor which reduces manufacturing costs, increases the versatility in manufacturing parts and subassemblies, and substantially reduces inventory costs.
In the prior art, one scheme used to drive the rollers in a powered roller conveyor is an endless belt guided by a series of guide rollers or pulleys and held against the surface rollers so that movement of the belt along the guide rollers drives the surface rollers. The belt is typically installed in such a manner that partial disassembly of the guide rollers and supporting structure is required to remove or install a belt. For this reason, the belts are very difficult to change when failure occurs and considerable down time may be experienced. Fixed guide rollers or pulleys and end pulleys are provided which are factory aligned to provide a positive contact between the endless belt, the guide rollers, and the surface rollers which is important in maintaining each of the surface rollers in a driving relationship with the belt and ensuring a smooth continuous flow of product across the conveyor. In some conveyors, intermediate full width guide rollers are provided which pivot only on one side to provide adjustment of tension between the belt and the surface rollers. However, the pivoting of the guide roller on one side has a tendency to skew the belt towards the center of the conveyor. This is undesirable as it places stress on the belt and tends to misalign the driving surface of the belt with the driven surface of the surface rollers. To eliminate this, crude guide posts have been provided in the prior art. These guide posts hold the belt in place by rubbing against the drive belt which increases wearing along the side of the belt. Therefore, a drive belt held in alignment with the surface rollers by the pivotable full length rollers have a tendency to wear rapidly and require constant adjustment to maintain a sufficient driving relationship with the majority of the surface rollers.
Most of the powered roller conveyors in the prior art include some sort of belt tightener to take up the slack which forms in the belt as it wears and ensure positive traction of the belt about the driving pulley or roller. Usually, two or more pulleys are provided and the belt is wound around them in a partial figure eight or the like. One prior art device includes a belt tightener having a pulley which may be mounted in any one of a series of holes spaced from one of the end pulleys. To tighten the drive belt, the belt tightener pulley must be removed from its mounting hole, the belt placed in proper tension and held as the tightener pulley is aligned with the drive belt and simultaneously inserted into a hole. As can be appreciated, it is quite difficult to create the proper tension in the belt at the same time that the pulley is aligned and inserted in one of the mounting holes. Furthermore, this device provides only incremental type of adjustment and it may not be possible to create the desirable tension due to the lack of a hole at the proper location. This can occur frequently as the length of the belt may change with use.
Applicant has succeeded in designing and constructing a conveyor which eliminates many of the problems of the prior art and which provides new features heretofore unavailable. Applicant's basic conveyor includes a straight section of gravity roller conveyor which may be later converted to a powered roller conveyor in the field. The basic structure has adjustable legs and small side frames. A center spine may be provided which extends the length of the conveyor to provide extra strength for those applications requiring the conveyor to carry heavy loads, or where power is added to the conveyor and the loads to be handled are significant enough to require the extra strengthening. Alternately, only center brackets may be provided to later mount the bearings which support a drive shaft and end pulley that are chain coupled or belt coupled to a gear motor output. A mounting plate is also provided for the later addition of a gear motor.
One of the features of applicant's conveyor is a new design for a guide pulley mount which incorporates a bolt-on tee bar mount and a free-riding cross bar support with adjustable tension spring for one or more guide pulleys. Each cross bar mount may be separately adjusted to achieve the desirable tension between its guide pulleys, the drive belt, and the rollers immediately above. This individual adjustment allows for a tension of zero to maximum at any of several places along the length of the conveyor and allowances may thereby be made for differently sized rollers, uneven wear, or other spot problems in the conveyor. The individualized construction also provides for the rapid replacement of any guide pulley or assembly which fails without shutting down the conveyor.
Both the tee bar mount and the cross bar may be canted or angled with respect to the rollers to orient the guide pulleys for use with tapered rollers in curved sections of conveyor. Typically, in the prior art, the tapered rollers have a non-tapered cylindrical section near the inside edge of each roller which contacts the driving belt. However, with applicant's new design guide pulleys and mount, the guide pulleys may be canted so that the endless belt is flush with the bottom angle of the tapered rollers. This reduces the cost for rollers in a curved section by eliminating the requirement of a straight cylindrical section on the rollers and also permits the rollers to be driven near their center. By driving the rollers near their center, less tension is required in the belt to achieve the same transfer of power as there is more belt in contact with each roller. Also, the drive belt obtains greater leverage due to the increased diameter of the roller at the point it is driven and each roller has an increased usable life as there is a greater circumference of roller over which the wearing of the drive belt is dispersed. In other words, the same amount of wear caused by the contact with the drive belt is dispersed over a greater amount of metal present in the larger circumference of the roller nearer its center.
Another new feature of applicant's invention includes a unique belt tightener which is elegantly simple in design but which has significant advantages over the prior art. For example, the belt tightener cooperates with applicant's new guide pulley mount to provide for easy and simple installation or removal of the endless belt in the field as is required to convert from a gravity roller to a powered roller conveyor or vice versa to meet the changing requirements of any installation. In the prior art, removal and replacement of the drive belt generally necessitates substantial disassembly of the guide rollers and their readjustment to ensure proper tension with the surface rollers. Another feature is that adjustment is rapid and provides for independent tension adjustment of each guide pulley mount in a direction perpendicular to that of the belt tightener. Also, applicant's belt tightener provides for infinitely variable adjustment instead of the incremental adjustment supplied by at least one belt tightener in the prior art.
An endless belt may be easily removed or installed from applicant's conveyor by creating slack with the belt tightener, retracting the guide pulley mounts and removal of one "pop-up" roller which is immediately above each fixed end pulley. Thus, the drive belt is not a permanent fixture of the conveyor which requires any significant dismantling before a broken or worn belt may be replaced or to accommodate the conversion from gravity to powered or vice versa.
In sum, applicant's new design conveyor significantly reduces the amount of steel and reinforcing which must be provided for any particular load, is quickly and easily changed in the field from gravity to powered or vice versa, introduces the concept of a center spine to eliminate the heavy and expensive side frames otherwise required, includes a new design for intermediate guide pulley mounts with individual tension adjustment between each set of guide pulleys and the belt and rollers, provides for guide pulleys to be mounted in a canted orientation to accommodate their use with standard tapered rollers in a curved section of conveyor, includes a new design belt tightener which provides for quick and easy removal of the belt without dismantling of the conveyor and which applies a tightening force perpendicular to the tension adjustment of the guide pulleys, all in one basic design conveyor with a minimum number of parts which reduces cost and increases versatility. These and other improvements and features are more fully explained in the drawings and description of the preferred embodiment.